GB2180671A

GB2180671A - Missile guidance system

Info

Publication number: GB2180671A
Application number: GB8308834A
Authority: GB
Inventors: Ronald George Guttridge
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 1983-03-30
Filing date: 1983-03-30
Publication date: 1987-04-01
Also published as: GB8308834D0; GB2180671B

Abstract

A missile guidance system using a radiometric tracker to detect the sky radiation reflected from a target has an RC output filter in the signal line between the tracker and the amplifiers to drive the missile steering controls. The time constant of the RC filter is reduced with decreasing target distance to allow the missile to manoeuvre with increasing agility as it closes on the target. Preferably R is varied with reference to the time of flight of the missile.

Description

SPECIFICATION Missile response rate modifier The present invention relates to missile guidance systems wherein the means for guiding the missile are controlled by signals derived from a radiometric tracker.

The use ofradiometrictracking to guide a missile to a target utilises the sky radiation reflected from the target in contrast to the emission ofthe target's su r- roundings. To maximisethe range overwhich a target may be detected, the radiometer in the missile is tuned to a wavelength which is relatively poorly absorbed by the constituents of the atmosphere.

It is known thatthe maximum range four a radiometric tracker is related to the input bandwidth B of the receiver and the output filter time consta nt T of the receiver by Ra(BT)141 andthusto maximisethe range available to the tracker the time consta nt T should bemaximisedfor a given value of B, as B normally has a value constrained by components within the receiver.

When a radiometrictracking missile is following a target the missile is steered to ensure thatthetarget is in the centre of the field of view ofthe tracker. Any deviation of the target from this central position in the field of view results in the generation of a guidance signal which is used to steerthe missile tore- turn the target to the centre of the field of view.

With the output time constant T optimised to provide, consistent with missi le agi I ity, the la rgest pos- sibledetection range forthe radiometer, the missile will be ableto followthe movements of even the mostagiletargetatlargetargetto missile distances.

As the missile closes on the target, however, movements of the target may be beyond the response rate of the missile due to the large time constant applied to the tracking system to ensure the largest possible detection range. Thus the requirement for a large time constant to maximise radiometer range conflicts with the increased rate of response the missile is required to exhibit as it closes on an agiletarget.

According to the present invention a homing missile includes a fixed input bandwidth radiometric tracker having an output filter, from which missile steering signals are derived, the time constant of which decreases with decreasing target distance to provide the missile with an increasing steering response rate as the missile closes on the target.

An embodimentofthe invention will nowbedes- cribed with reference to the following drawings, in which: Figure 1 shows schematically a sub munition having a radiometric tracker being released from a carrier above a target.

Figure2 shows schematically a sub munition tracking and steering system having a response rate modifier.

In Figure 1 a sub munitions carrier 1 isfallingtow- ardstheground ata speed determined bythepara- chute 2 after release from an aircraft (not shown). At a predetermined height above the ground, measured bythetimethe carrier has been falling from the aircraft on an internal clock (not shown), a sub mun ition, 3, is released. To establish a suitable horizontal flying speed, the sub munition is ejected from the carrier by a propellant charge, 11 The sub munition 3 is guided to the target,10, by a radiometrictracker4 which locks on to sky radiation 12 reflected by the target. The radiometric tracker steers the submunition towards the target by means of aerodynamic control surfaces 5.Within the sub munition a timer (not shown) measures the time of flight after release from the carrier 1 at a predetermined height and horizontal speed and a corresponding reduction is made in the output time constant of the radiometer to allow steering corrections to be made more rapidly.

In Figure 2 the radiometertracking and steering signal system forthe submunition 3 of Figure 1 is shown schematically.

Aconicallyscanned parabolic mirror, 21, rotates as shown by arrow T about the boresight line 22, with the axis of the mirror offset, 23. Radiation is reflected by the mirror into a horn aerial 24 and along a waveguide 25 to a mixer and intermediate frequency amplifier 26, where the signal is mixed with a signal derived from a local oscillator27,the intermediate frequency signal is then fed to a detector 28 which is a.c. coupled to an amplifier 29 and a negative unity gainamplifier30.Amirrorscan positionsensor31 provides a mirror position reference signal which is split by reference generator 32 into reference signals with a p/2 phase difference.The reference signals are then used in the synchronous detection of azimuth,33, and elevation, 34, steering signals from the output of the amplifiers 29 and 30. Low pass RC filters 35 and 36 in the output from the synchronous detectors have variable resistances (not shown) activated by a timer 37 started on release of the sub munition from the carrier. The variable resistances arevariedsothatthecutofffrequencyofthelow pass filters rises with time of flight of the sub munition thus permitting increasingly rapid manoeuvring signalsto be transmitted viathe amplifiers 38,39 to the aerodynamic control surfaces ofthe submunition.

1. A homing missile including a fixed bandwidth radiometrictrackerfrom which missile steering signals are derived having an RC outputfilterthe time constant of which decreases with decreasing target distance to provide the missile with an increasing steering response rate as the missile closes on the target.

2. A homing missile as claimed in claim 1 wherein the decreasing target distance is indicated by a time of flight clock activated when the missile is launched.

3. A homing missile as claimed in claim 1 wherein the decreasing target distance is indicated by a barometric heightsensorwithin the missile.

4. A homing missile as claimed in claim 2 orclaim 3 wherein the time constant of the RC output filter is

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Missile response rate modifier The present invention relates to missile guidance systems wherein the means for guiding the missile are controlled by signals derived from a radiometric tracker. The use ofradiometrictracking to guide a missile to a target utilises the sky radiation reflected from the target in contrast to the emission ofthe target's su r- roundings. To maximisethe range overwhich a target may be detected, the radiometer in the missile is tuned to a wavelength which is relatively poorly absorbed by the constituents of the atmosphere. It is known thatthe maximum range four a radiometric tracker is related to the input bandwidth B of the receiver and the output filter time consta nt T of the receiver by Ra(BT)141 andthusto maximisethe range available to the tracker the time consta nt T should bemaximisedfor a given value of B, as B normally has a value constrained by components within the receiver. When a radiometrictracking missile is following a target the missile is steered to ensure thatthetarget is in the centre of the field of view ofthe tracker. Any deviation of the target from this central position in the field of view results in the generation of a guidance signal which is used to steerthe missile tore- turn the target to the centre of the field of view. With the output time constant T optimised to provide, consistent with missi le agi I ity, the la rgest pos- sibledetection range forthe radiometer, the missile will be ableto followthe movements of even the mostagiletargetatlargetargetto missile distances. As the missile closes on the target, however, movements of the target may be beyond the response rate of the missile due to the large time constant applied to the tracking system to ensure the largest possible detection range. Thus the requirement for a large time constant to maximise radiometer range conflicts with the increased rate of response the missile is required to exhibit as it closes on an agiletarget. According to the present invention a homing missile includes a fixed input bandwidth radiometric tracker having an output filter, from which missile steering signals are derived, the time constant of which decreases with decreasing target distance to provide the missile with an increasing steering response rate as the missile closes on the target. An embodimentofthe invention will nowbedes- cribed with reference to the following drawings, in which: Figure 1 shows schematically a sub munition having a radiometric tracker being released from a carrier above a target. Figure2 shows schematically a sub munition tracking and steering system having a response rate modifier. In Figure 1 a sub munitions carrier 1 isfallingtow- ardstheground ata speed determined bythepara- chute 2 after release from an aircraft (not shown). At a predetermined height above the ground, measured bythetimethe carrier has been falling from the aircraft on an internal clock (not shown), a sub mun ition, 3, is released. To establish a suitable horizontal flying speed, the sub munition is ejected from the carrier by a propellant charge, 11 The sub munition 3 is guided to the target,10, by a radiometrictracker4 which locks on to sky radiation 12 reflected by the target. The radiometric tracker steers the submunition towards the target by means of aerodynamic control surfaces 5.Within the sub munition a timer (not shown) measures the time of flight after release from the carrier 1 at a predetermined height and horizontal speed and a corresponding reduction is made in the output time constant of the radiometer to allow steering corrections to be made more rapidly. In Figure 2 the radiometertracking and steering signal system forthe submunition 3 of Figure 1 is shown schematically. Aconicallyscanned parabolic mirror, 21, rotates as shown by arrow T about the boresight line 22, with the axis of the mirror offset, 23. Radiation is reflected by the mirror into a horn aerial 24 and along a waveguide 25 to a mixer and intermediate frequency amplifier 26, where the signal is mixed with a signal derived from a local oscillator27,the intermediate frequency signal is then fed to a detector 28 which is a.c. coupled to an amplifier 29 and a negative unity gainamplifier30.Amirrorscan positionsensor31 provides a mirror position reference signal which is split by reference generator 32 into reference signals with a p/2 phase difference.The reference signals are then used in the synchronous detection of azimuth,33, and elevation, 34, steering signals from the output of the amplifiers 29 and 30. Low pass RC filters 35 and 36 in the output from the synchronous detectors have variable resistances (not shown) activated by a timer 37 started on release of the sub munition from the carrier. The variable resistances arevariedsothatthecutofffrequencyofthelow pass filters rises with time of flight of the sub munition thus permitting increasingly rapid manoeuvring signalsto be transmitted viathe amplifiers 38,39 to the aerodynamic control surfaces ofthe submunition. CLAIMS

4. A homing missile including a fixed bandwidth radiometric tracker substantially as herein described and as illustrated with reference to Figures 1 and 2.

4. A homing missile as claimed in claim 2 orclaim 3 wherein the time constant of the RC output filter is varied by varying R with reference to the time offlight ofthemissileorthe height ofthe missile.

5. A homing missile including a fixed bandwidth radiometric tracker substantially as herein described and as illustrated with reference to Figures 1 and 2.

Amendmentstotheclaims have been filed, and have the following effect: *(a) Claims 3-5 above have been deleted ortextually amended.

*(b) Newortextually amended claims have been filed asfollows:

3. A homing missile as claimed in claim 2 wherein the time constant of the RC output filter is varied byvarying Rwith reference to thetimeofflight ofthe missile.